1. Field of the Invention
The present invention relates to a semiconductor, and more particularly to an apparatus and a method for heat-treating a semiconductor substrate, capable of applying different temperatures to a substrate.
2. Description of the Conventional Art
Studies for integrated semiconductor devices in which various function devices are integrated on a semiconductor substrate have been performed. For example, a system on chip into which a logic device such as a micro controller unit (MCU) and a memory device such as a random access memory (RAM) are composed is one of the integrated semiconductor devices. Therefore, semiconductor devices which have different electric properties are fabricated on a single semiconductor substrate, and thus the semiconductor substrate requires a heat treatment with different heat treatment conditions (temperatures) in the semiconductor device fabrication process.
More specifically, when forming a source and a drain, a heat treatment is required for impurity diffusion after impurity implantation. Here, the optimum heat-treatment temperature in a memory cell unit is 1000xc2x0 C., while the optimum temperature in a logic unit is 900xc2x0 C. Thus, the impurity implantation and diffusion process of the memory cell cannot be concurrently performed with that of the logic unit, but such process should be performed Mice as in which the source and drain of the memory cell has to be formed first and followed by forming the source and drain of the logic unit.
Further, to fabricate transistors which have different threshold voltages on the same semiconductor substrate, it is necessary to make a gate oxidation film of which portions have different thickness, which requires a heat treatment (heat oxidation) to thereby control portions of the semiconductor substrate to have different temperatures. That is, in general the gate oxidation film is formed by which high-purity oxygen is implanted into a silicon substrate and a heat treatment is applied thereto. Here, the higher the temperature of the semiconductor substrate becomes, the more rapid the growth speed of the oxidation film becomes. On the other hand, the lower the temperature of the semiconductor substrate becomes, the slower the growth speed of the oxidation film becomes.
A process of forming a film (a gate oxidation film) of which portions have different thickness on the conventional semiconductor substrate with the same material will be described as follows. First, FIG. 1 is a schematic diagram of a conventional heat-treating apparatus. As shown therein, a wafer holder 102 for supporting a semiconductor substrate or a wafer 101 is placed at a lower side in a chamber 100 and halogen lamps 103 serving as a heating device are provided at an upper side therein, wherein a source gas is flowed from one side of the chamber 100, as in the direction of the arrow in FIG. 1, to the other side thereof.
In the process of forming the oxidation film via a rapid heat-treatment, a growth rate of the oxidation film is affected by the temperature of the substrate. In other words, as the temperature of the substrate increases, the oxidation rate also increases, while as the temperature thereof decreases, the oxidation rate slows down. Therefore, when forming the heat-oxidation film by using the conventional heat-treatment apparatus, the semiconductor substrate 101 uniformly receives the heat as a whole from the heating device, which results in the formation of the film with the uniform thickness on the semiconductor substrate 101. Accordingly, there is required an additional process to form a heat oxidation film of which portions have different thickness on the same semiconductor substrate, which will be described as follows.
More specifically, in FIG. 2A, using the conventional heat-treatment apparatus in FIG. 1, a thick oxidation film 201 is formed on an entire surface of the semiconductor substrate in a relatively high temperature condition. After forming a photoresist film on the oxidation film 201, a photoresist pattern 202 is formed by patterning the photoresist film so that the photoresist film remains on an area where an oxidation film is to be thickly formed, and a portion of the thick oxidation film 201 that the oxidation film is to be thinly formed is removed. The resultant pattern is shown in FIG. 2. Then, as shown in FIG. 2C, on a bare surface of the semiconductor substrate 101 from which the thick oxidation film 201 has been removed, an oxidation film 203 which is thinner than film 201 is formed at a relatively low temperature, and then the photoresist pattern 202 remaining on the thick oxidation film 201 is removed by a plasma ashing method. Eventually, as shown in FIG. 2C, the oxidation film having the portions 201, 203 with different thicknesses is formed on the single semiconductor substrate 101.
In the conventional heat-treatment process, therefore, the semiconductor substrate is composed of an area A and an area B, and the areas A, B should be heat-treated at different temperatures. Accordingly, for example, the area A is protected with a mask such as the photoresist pattern and the area B is only heat-treated at an optimum temperature, and then the area A is heat-treated at an optimum temperature with the area B being protected with the mask, which requires several heat-treatment processes. Thus, the conventional process for fabricating the semiconductor device is complicated, the semiconductor substrate intensively receives thermal stress and a throughput of semiconductor device fabrication unavoidably decreases.
Further, the conventional process, for forming a gate oxidation film of which portions have different thicknesses on a single semiconductor substrate, is quite complicated due to the additional processes such as a photolithography, an etching and a rinsing. Also, due to the plasma ashing performed to remove a photoresist film after performing the photolithography process, the oxidation film is damaged which results in degradation of the film property and thus deterioration of the reliability of the semiconductor device fabricated by using the thusly formed oxidation film.
Accordingly, the present invention is directed to an apparatus and a method for heat-treating a semiconductor substrate which obviates the problems and disadvantages due to the conventional art.
An object of the present invention is to provide an apparatus and a method for heat-treating a semiconductor substrate capable of heat-treating a semiconductor substrate in which portions have different optimum heat-treating conditions by a single heat treatment process, as well as satisfying the optimum heat-treating conditions.
Another object of the present invention is to provide an apparatus and a method for heat-treating a semiconductor substrate that form a film on the semiconductor substrate of which portions have different thickness.
Still another object of the present invention is to provide an apparatus and a method for heat-treating a semiconductor substrate that facilitate a semiconductor device fabricating process by omitting other processes which are necessary to the conventional art, such as a photolithography, an etching, a plasma ashing and a rinsing processes, as well as form an oxidation film of good quality.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an apparatus for heat-treating a semiconductor substrate includes a chamber of a refractory material, a support plate located at a lower side in the chamber for supporting the semiconductor substrate, a heating device disposed at an upper side in the chamber, and a heat resistance mask provided between the support plate and fabricated to have different heat transmission rates of portions thereof.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide and further explanation of the invention as claimed.